Mayflies Swarm in Wisconsin: Are Shoveled Up Like Snow

Mayflies have begun to swarm in Wisconsin and other states near the Mississippi River and they can create a dangerous mess. The mayflies are attracted to light and form congregations of thousands that swarm through the air or pile up in thick masses on the roads, houses and other structures. Cars running over the masses of mayflies slide in the slush of the squished bodies like sliding through snow slush in the winter.

The swarms occur throughout the summer with the first massive swarm of this year being reported on July 20. Another minor swarm was reported on July 24 and it is expected there will be many more to come until the end of August.

The mayflies lay their eggs on water during the summer and then the young fall to the floor of the Mississippi River to develop. During the following summer, the eggs hatch and swarms of mayflies emerge. Within about 48 hours, the mayflies shed their exoskeletons, mate, and then the females deposit their eggs on the waters of the Mississippi River to complete the cycle. After mating, all the adult mayflies that emerged that summer die. After spending a year in the silt on the bottom of the Mississippi River, they spend a few glorious hours flying and checking each other out to mate, and then they complete the act and die. This can certainly be viewed as an example in which each and every moment of life counts.

There are only massive, troublesome swarms during some summers, just like there are only some winters with massive storms and amounts of snowfall. The determining factor in whether the swarms will be massive or smaller is the mayflies are sensitive to pollutants and oxygen levels in the waters of the Mississippi River. The Clean Water Act of 1978 was instrumental in producing better water conditions for the emergence of more mayflies. There was a waning in mayfly swarms between 1920 and 1978 in some areas along the Mississippi River. Whether there are mayfly swarms in the summer or not can be used as a measure of the condition of the water of the Mississippi River.

The National Weather Service provides information on mayfly swarms and makes forecasts as a public service. They even maintain a place on their website for people to tell their stories and post interesting pictures (see source below). The swarms of mayflies can be so thick and massive that the National Weather Service even follows the swarms on their radar screens.

People who live in Wisconsin and other northern states near the Mississippi River are not put off by the massive piles of mayflies that accumulate during the swarms. Even though the bugs are annoying while they are flying through the air, the clean-up of the piles can be handled just like snow, and everyone in Wisconsin knows how to take care of massive piles of snow. It has also been observed that the mayflies can lay their eggs in other types of liquids besides water. Some have even observed the mayflies laying their eggs in glasses of beer, and everyone in Wisconsin knows there are plenty of glasses of beer available during the summer for this possibility.